JPH02229149A - Production of aromatic urethane - Google Patents

Abstract

PURPOSE:To obtain aromatic urethane having high quality in high yield by reacting aromatic nitro compound, hydroxyl group-containing organic compound and carbon monoxide in the presence of platinum metal/Lewis acid/nitrogen- containing heteroaromatic compound catalyst system. CONSTITUTION:Aromatic nitro compound is reacted with hydroxyl group- containing organic compound and carbon monoxide in the presence of catalyst system (e.g. Pd/C-FeCl3-pyridine system catalyst) composed of platinum metal as principal catalyst, Lewis acid as promotor and nitrogen-containing heteroaromatic compound as ligand in aliphatic hydrocarbon system solvent (e.g. n-hexane) at 100-250 deg.C to afford the aimed substance. In the reaction, Lewis acid deteriorating expensive platinum metal and generated substance containing said metal as principal catalyst is efficiently separated by fixing platinum metal as principal catalyst in reaction vessel. Aromatic urethane is especially useful as raw material of producing polymethylene polyphenyl polyisocyanate as raw material of polyurethane by non-phosgene method.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing aromatic urethane compounds, and in particular, polymethylene polyphenyl polyisocyanate (hereinafter abbreviated as PMPP I), which is a raw material for polyurethane, is processed into a non-phosgene compound. The present invention relates to a method for producing an aromatic urethane compound, which is a starting material when produced by a method.

Specifically, in the production of aromatic urethane, which involves reacting an aromatic nitro compound, a hydrous acid group organic compound, and carbon monoxide in the presence of a platinum group metal/Lewis acid/nitrogen-containing heteroaromatic compound catalyst system, This invention relates to an improved method that allows easy recovery and reuse of products and prevents quality deterioration during product recovery.

(Prior technology) PMP is used in large quantities as a raw material for polyurethane
PI has conventionally been produced industrially by a phosgene method in which phosgene is allowed to act on an aromatic amine obtained by reducing an aromatic nitro compound. However, this method has problems such as the use of toxic phosgene, the need for expensive chlorine to synthesize phosgene, and the production of a large amount of hydrogen chloride as a by-product.

Therefore, methods for synthesizing P liver PI by a non-phosgene method that does not use phosgene have been actively researched.

One of the non-phosgene methods involves using an aromatic nitro compound as a starting material and passing through three steps: carbonylation, condensation, and thermal decomposition. For details, see aromatic nitro compounds,
Carbonylation (to synthesize aromatic urethane by reacting carbon monoxide and a hydrous acid group organic compound in the presence of a catalyst),
Next, this urethane is crosslinked by a condensation reaction with a methylenating agent such as formaldehyde to synthesize a polyurethane compound (condensation), and the hydrous acid group organic compound (alcohol or phenol) is eliminated from this polyurethane compound (thermal decomposition). This is a method to obtain PMPPT of .

Taking the synthesis of MDI (methylene diphenyl diisocyanate), which is a typical example of PMPP I, as an example, the above reaction route is shown in the following reaction formula.

Condensation: Thermal decomposition: MDII-Methylenediphenylcica-bamate The present invention relates to a method for producing urethane compounds such as EPC by a reaction corresponding to the carbonylation step of the above reaction route.

A method for producing an aromatic urethane by carrying out the above carbonylation step in the presence of a catalyst system consisting of a platinum group metal (main catalyst), a Lewis acid (co-catalyst) and a nitrogen-containing heteroaromatic compound (ligand) is known. It is. This urethane synthesis method has the advantage that the catalyst can be recovered, the yield is high, and corrosion of the reaction equipment is suppressed.

After this reaction, the catalyst and aromatic urethane are recovered from the resulting reaction mixture, the catalyst is reused in the carbonylation reaction, and the aromatic urethane is thermally decomposed through the condensation step in the next step.
Converted to DI. Therefore, industrially, it is important to recover the catalyst in a reusable state and to recover the aromatic urethane product with high purity and high yield so that it can be used in the next step. With these points in mind, the following methods have been proposed in the past.

Japanese Patent Publication No. 56-3861 states that after the completion of the reaction, the catalyst insoluble in the reaction solution was separated and recovered by filtration while hot, and then the filtrate was cooled to recover the precipitated aromatic urethane product. A method is disclosed in which the mother liquor is used together with the recovered catalyst in the next urethane synthesis.

JP-A-53-137929 describes a method for purifying the aromatic urethane obtained by the above method by treating it with an acidic aqueous solution. This improves the thermal stability of the urethane product, and suppresses the by-product of tar substances other than the target isocyanate in the next thermal decomposition step.

Furthermore, a method is also known in which, after the reaction is completed, the insoluble catalyst is recovered by hot filtration or the like, and the filtrate is concentrated or distilled to recover the aromatic urethane.

(Problems to be Solved by the Invention) In order to improve contact with the reaction substrates (aromatic nitro compounds, hydrous acid group organic compounds, and carbon monoxide), the carbonylation catalyst is mainly used in the case of a heterogeneous system. The catalyst used is a platinum group metal supported on a fine powder carrier.

However, since the fine powder catalyst is a powder, it is difficult to handle, and the process requires a catalyst separation step, which is uneconomical. Furthermore, even if a catalyst separation process is provided, it is difficult to separate and recover the catalyst because it is a fine powder.For example, when separating by filtration using a filter, troubles such as clogging of the filter surface occur, and when using centrifugation, the overflow side There are drawbacks such as the catalyst flowing out and having an adverse effect on subsequent processes, and increasing the loss of expensive platinum group metal catalysts.

Furthermore, in the above-mentioned urethane synthesis method, it has been common to use a large excess of a hydrous acid group organic compound as a reaction substrate, which also serves as a solvent.

This hydrous acid group organic compound has a high ability to dissolve catalysts, especially Lewis acids. Therefore, even if the insoluble catalyst is separated from the reaction solution by filtration after the reaction is completed, a considerable amount of the catalyst will still be dissolved in the filtrate and will be mixed into the filtrate. In some cases, less than half of the Lewis acid is recovered by filtration, with most of the Lewis acid remaining in the filtrate. Therefore, when aromatic urethane is recovered from this filtrate by distillation, the aromatic urethane product is thermally degraded by the Lewis acid in the catalyst remaining in the filtrate, resulting in a decrease in the yield and deterioration of the quality of the urethane product.

In particular, aromatic urethane (EPC) is a raw material for MDI synthesis.
When recovering , it is difficult to apply the crystallization method as disclosed in Japanese Patent Publication No. 56-3861, so a distillation method must be used.

FIG. 1 shows the residual rate of RPC when various amounts of Lewis acid pecI 3 were added to EPC, which is a urethane product, and the mixture was heat-treated at 110° C. for 1 hour. The figure shows that the greater the amount of Lewis acid coexisting in urethane, the lower the residual rate.In other words, in the coexistence of Lewis acid, the thermal stability of urethane decreases and it undergoes thermal deterioration, but the larger the amount of Lewis acid coexisting, the more the urethane coexists. It can be seen that the higher the temperature, the more severe the thermal deterioration becomes.

Therefore, when recovering urethane products by distillation as described above, as the distillation progresses, the amount of urethane in the distillation pot decreases, and the relative amount of the catalyst that does not distill out to the urethane increases, so at the end of the distillation, the amount of urethane is thermal deterioration becomes significant and the yield decreases.

Furthermore, since the amount of catalyst remaining in the filtrate is large, the amount of catalyst recovered as solid content by filtration is also low, and it becomes necessary to add a new catalyst for reuse.

Even when the urethane product is recovered from the filtrate by cooling and crystallization, a large amount of catalyst remains in the filtrate as described above, and this precipitates out together with the urethane product, resulting in poor quality of the recovered urethane product. worsen. In addition, the catalyst and urethane product remain in a coexisting state in the mother liquor after crystallization separation.
If this mother liquor is used in the next reaction, thermal deterioration of the urethane product is unavoidable.

The purpose of the present invention is to solve the above-mentioned problems in the method for producing aromatic urethane by the carbonylation reaction, and specifically, to eliminate the need for the recovery step of the main catalyst after the reaction, and to By avoiding metal loss and improving the separation efficiency between aromatic urethane products and catalysts (particularly Lewis acids that degrade the products), catalyst reuse rates and aromatic urethane quality/yields can be improved. The goal is to improve.

(Means for Solving the Problems) The present inventors have studied methods for efficiently separating catalysts, particularly expensive platinum group metals that are the main catalyst, and Lewis acids that degrade products from aromatic urethane products. As a result of repeated efforts, by fixing the platinum group metal in the reactor and allowing an aliphatic hydrocarbon solvent to coexist during the reaction, the separation and recovery process of the platinum group metal was not necessary, and at the same time, the Lewis acid became insolubilized. have found that they can be efficiently separated from urethane products that remain in solution.

This avoids loss of expensive platinum group metals, improves Lewis acid recovery, and facilitates reuse of the main catalyst and co-catalyst. At the same time, since only a trace amount of Lewis acid exists in the separated aromatic urethane, there is no decrease in yield due to thermal denaturation even when the urethane is recovered by distillation, and the product is recovered with high purity and high recovery rate. It is also possible to do so.

The gist of the present invention is to use an aromatic nitro compound, a hydrous acid group organic compound, and carbon monoxide as main catalysts, and a platinum group metal,
In a method for producing aromatic urethane by reacting in the presence of a catalyst system consisting of a Lewis acid as a promoter and a nitrogen-containing heteroaromatic compound as a ligand, in a reactor in which the platinum group metal is fixed. , is a method for producing aromatic urethane, characterized in that the reaction is carried out in the coexistence of an aliphatic hydrocarbon solvent.

(Function) One of the features of the present invention is that the platinum group metal, which is the main catalyst for the carbonylation reaction, is fixed in the reactor.

The present inventors conducted a carbonylation reaction using Pd/C-FeC (!3-pyridine-based catalyst) using PdCQ in advance.
In the apparatus in which the reaction was carried out using z as a catalyst, Pd
They discovered that even if the reaction is carried out without adding the source, the same reaction results can be obtained as when the source is added, and furthermore, the effect persists in subsequent reactions. As a result of intensive investigation into this phenomenon, it was determined that the cause was that when PdCQ was reduced by carbon monoxide or the like and precipitated as metal PcT, a portion of it adhered to the inner wall of the device. That is, the fact that a small amount of Pd attached to the inner wall is effective as a catalyst indicates that there is no need to use a finely powdered catalyst or a homogeneous catalyst to improve the catalytic effect with the reaction substrate.

Based on this, we investigated in detail the effect of the amount of platinum group metal as the main catalyst in the above reaction on the reaction results using a separate apparatus, and found that other than Pd/C=O (i.e., the main catalyst is pure jD), Almost the same good reaction results are maintained, and only a very small amount of Pd is required for the reaction, and the reaction results are better than Pd.
It was found that it was not dependent on quantity.

Regarding the batch synthesis of phenyl urethane (ethyl N-phenylcarbamate) by the reaction of nitrobenzene, ethanol, and CO, the reaction results in a reactor in which the platinum group metal as the main catalyst was fixed according to the present invention were compared with the conventional method. Pd/
An experiment was conducted to compare the results with a method in which C was added to the reactor. The reaction conditions are as follows.

Charge amount of nitrobenzene: 10 mmole Charge amount of pyridine: 5 mmole Charge amount of ethanol: 15 ml Reaction temperature: 160'c Reaction time
3 hours CO initial pressure 80kg/cm2GFeC
The amount of Q:l added was varied within the range of 0 to 2.5 mmole.

The reaction results (yield of phenyl urethane) are expressed as F e CQ
The results plotted against the addition amount of 3 are shown in FIG.

In FIG. 2, . indicates the reaction results of the method of the present invention, and O indicates the reaction results of the conventional method. In the method of the present invention, a reactor is used which is coated with Pd on the inner wall by performing a synthesis experiment using PdC (!z as the main catalyst) as a reactor from the outside.
The reaction was carried out without adding C.

On the other hand, in the conventional method, the same type of equipment without Pd coating is used, and 5% Pd/C is applied from the outside to 0 in terms of Pd.
．． 05 mg-atom was added to carry out the reaction.

From Figure 2, there is almost no difference in the yield of phenyl urethane between the method of the present invention (・) and the conventional method (○), and even Pd fixed on the inner wall of the device has the same catalytic effect as Pd supplied from the outside. I understand that. It was also found that the reaction rate was determined by the amount of PeCQx and was not dependent on the amount of Pd. That is, Pd only needs to exist in a very small amount in the reactor, and there is no need to supply a certain amount from outside.

Methods for fixing platinum group metals in the reactor include coating the inner surface of the reactor with platinum group metals by means such as plating or thermal spraying, or lining the reactor with platinum group metals alone or supported on a carrier. Various methods are available, such as fixing the metal into an inner cylinder, wire mesh, block, etc. in the reactor, or fixing a fixed bed in which the metal is supported on a carrier in the reactor. This is possible, and as shown in the Examples below, either method can provide results equivalent to those obtained by externally supplying a conventional platinum group metal.

Furthermore, since the platinum group metal exhibits a catalytic effect if only a very small amount is present in the reaction system, there is no particular uniformity in the amount of the platinum group metal fixed in the reactor.

In this way, according to the present invention, by fixing the main catalyst, a platinum group metal such as Pd, in the reactor by some means and conducting the reaction, it is possible to obtain reaction results equivalent to the conventional method of constantly supplying from the outside. . Furthermore, since the amount of platinum group metal required for catalytic action is extremely small, a reactor in which the main catalyst is fixed can exhibit catalytic action for a long period of time. Therefore, regardless of whether the reaction is batchwise or continuous, it is possible to sustain the reaction for a long period of time without having to perform troublesome operations such as supplying the main catalyst to the reactor, recovering it after the reaction, and in some cases regenerating it. This method is economically advantageous compared to the conventional method because the loss of the expensive main catalyst is very small.

Another feature of the present invention is that in the production of aromatic urethane by the carbonylation reaction, the catalyst (particularly Lewis acid) and the urethane product can be separated by conducting the reaction in the presence of an aliphatic hydrocarbon solvent. It's about making it easier.

Aliphatic hydrocarbon solvents that can be used in the present invention include linear or branched alkanes as well as cycloalkanes. Specific examples include n-benkune, n-hexane, n-
Hebutane, n-octane, n-nonane, n-decane, 0-
undecane, n-dodecane, n-1-lysocane, n-
Tetradecane, n-pentadecane, isopentane, isohexane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, 2.3-dimethylpenkune, 2-ethylhexane, cyclobenkune, cyclohexane, cyclohebutane, cyclo octane, cyclononane,
Methylcyclobencune, methylcyclohexane, ■, 1
-dimethylcyclohexane, 1,2 dimethylcyclohexane, 13-dimethylcyclohexane, 1,4-dimethylcyclohexane and the like. Isomers of these compounds or mixtures of two or more solvents can also be used.

In conventional processes, as mentioned above, a significant portion of the catalyst, especially the Lewis acid, is present in solution after the reaction.

Therefore, the catalyst cannot be completely separated from the product by simply filtering the reaction mixture, and the catalyst remaining in the urethane product causes deterioration of the product.

Therefore, in order to improve the yield and quality of the urethane product and to increase the recovery of the catalyst, it is necessary to separate the catalyst from the urethane product as completely as possible, and according to the present invention: By adding an aliphatic hydrocarbon solvent to the reaction system and carrying out the reaction in its presence, almost the entire amount of the catalyst can be recovered as a solid content during filtration after the reaction. Aliphatic hydrocarbon solvents are particularly suitable for this purpose because they are capable of dissolving the urethane product without dissolving the catalyst and are inert to the reaction. Furthermore, the coexistence of this solvent during the reaction does not have an adverse effect on the reaction.

The amount of the aliphatic hydrocarbon solvent added is the amount necessary to substantially completely insolubilize the catalyst, particularly the Lewis acid, which can be dissolved in the unreacted hydrous acid group organic compound after the reaction. For this purpose, it is preferable to use the above-mentioned solvent in a volume ratio of 1=1 or more to the amount of hydrous acid groups charged in the reactor to the amount of organic compound.

The substances used, reaction conditions, etc. other than those mentioned above may be the same as those for the conventional carbonylation reaction, but will be briefly explained below.

The aromatic nitro compound serving as the main raw material is a compound containing at least one nitro group directly bonded to an aromatic ring, and is not limited to a mononitro compound, but may be a polynitro compound. The aromatic ring may be monocyclic or polycyclic, and compounds containing various substituents in addition to the nitro group can also be used as raw materials.

As the hydrated acid group organic compound, any of monohydric and polyhydric alcohols and monohydric and polyhydric phenols containing primary, secondary, and secondary hydroxyl groups can be used.
In the case of producing an aromatic urethane compound as a raw material for producing an aromatic polyisocyanate compound, ethanol or methanol is most suitable.

The platinum group metal used as the main catalyst in this reaction is selected from the simple metals palladium, ruthenium, rhodium, platinum, osmium, and iridium, and may be in any form as the metal or supported on a carrier. Industrially, relatively inexpensive palladium and ruthenium are most suitable.

Further, as the Lewis acid of the co-catalyst, it is possible to use a compound of an element selected from Groups A to II of the Periodic Table of Elements and subgroups IB-VB, which can carry out a redox reaction under the reaction conditions.

The nitrogen-containing heteroaromatic compound as a ligand may be unsubstituted or may contain a substituent that is inert under the reaction conditions. Also, acid addition salts of nitrogen-containing heteroaromatic compounds,
Quaternary salts or oxides can also be used.

These nitrogen-containing heteroaromatic compounds form a complex with a Lewis acid, so among the components of the catalyst system, the Lewis acid and the nitrogen-containing heteroaromatic compound can be used in the form of a complex by reacting them in advance. .

The carbonylation reaction is preferably carried out using carbon monoxide at a molar ratio of at least three times the nitro group of the aromatic nitrated metal as the main raw material.

It is necessary to use the hydrous acid group organic compound in an amount equal to or more than the nitro group. However, if it is used in large excess, the amount of dissolved catalyst increases, and the amount of aliphatic hydrocarbon solvent required to separate the catalyst as an insoluble component in the present invention increases. Therefore, it is preferable to use the hydrous acid group organic compound in a molar ratio of 1:1 to 10:1 to the nitro group.

According to the present invention, since an aliphatic hydrocarbon solvent is allowed to coexist in the reaction system, the amount of a hydrous acid group organic compound such as alcohol may be used in a smaller amount than in the past.

There are no particular restrictions on the charging method or order of addition of the reactants and catalyst, and they can be changed within the limitations of the equipment used. The reaction may be carried out batchwise, semi-continuously or continuously.

As the reaction solvent, an aliphatic hydrocarbon solvent is used as described above, but other solvents may be present in small amounts.

The reaction temperature is within the range of 100 to 250°C, especially 140 to 1
It is preferably within the range of 90'C. The reaction pressure is 10 to 1000 kg/cJ-G as the partial pressure of carbon monoxide, especially 3
The range of 0 to 300 kg/at (-G is preferable.The reaction time depends on the type of reactant used, the reaction temperature, the reaction pressure,
Generally, 0.5 to 10 hours is sufficient, although it varies depending on various factors such as the type and amount of catalyst and the reaction equipment.

The treatment after the completion of the reaction can be carried out, for example, as follows.

The reaction mixture is first cooled to room temperature and depressurized. Since the catalyst is insolubilized by the presence of the aliphatic hydrocarbon solvent,
When the reaction mixture is filtered, the catalyst, especially the Lewis acid, can be recovered almost completely as solids. The recovered catalyst can be recycled as it is or after being purified by an appropriate method such as solvent washing and having its composition adjusted.

If the insolubilization of the catalyst is not sufficient, this type of solvent can also be added after the reaction to achieve complete separation of the catalyst. When adding an aliphatic hydrocarbon solvent two or more times, the solvents used may be the same or different.

Insolubilization of Lewis acids requires the use of a large amount of aliphatic hydrocarbon solvents and hydrous acid group organic compounds such as anti-alcohols, which also serve as solvents, so the amount of hydrocarbon solvent required for insolubilization becomes extremely large, or It is necessary to concentrate the reaction mixture in advance, which is economically disadvantageous.

According to the method of the present invention, the platinum group metal component of the main catalyst is fixed in the reactor, and the loss of other catalyst components is very small, so the amount of catalyst added when the catalyst is used in circulation is much smaller than before. Not only that, but the process of recovering the main catalyst becomes unnecessary.

In addition to filtration, the catalyst can be separated by any solid-liquid separation means such as centrifugation and decantation.

When the catalyst is separated as described above, a reaction liquid containing almost no catalyst is obtained. The aromatic urethane product is recovered from this reaction solution by an appropriate method such as distillation or crystallization. Since there is no catalyst (particularly a Lewis acid), even if urethane is recovered by distillation, there will be no reduction in product yield or quality deterioration due to thermal denaturation or the like. Thereby, a substantially pure aromatic urethane product can be obtained in high yield without any particular purification.

Hereinafter, the present invention will be explained in more detail with reference to Examples. The conversion rate and yield were calculated from the results of measurements by liquid chromatography.

Example The reactor used in this example was a pressurized flow reactor with an internal volume of 200 m equipped with a stirrer, and a platinum group metal as the main catalyst was fixed in the reactor by the method shown below. Nitrobenzene 0.8 mol/I was added to a mixed solvent of ethanol and an aliphatic hydrocarbon solvent at a volume ratio of 1/2.
A solution containing 0.4 mo1712 of pyridine, and 0.2 mo+/12 of anhydrous ferric chloride was used as the reaction solution. This reaction solution was heated to 160°C and 100 kg/hr at a flow rate of 25 ml/hr (average residence time: 4 hours).
cm2-(under H conditions, CO gas 5.5Nj!/hr
The reaction was carried out continuously for 120 hours while supplying the same to the reactor. Initial pressurization of the reactor was performed with CO gas. After the reaction was completed, the reactor was cooled to room temperature, evacuated, and replaced with nitrogen gas. The resulting reaction mixture was filtered and separated into insoluble and soluble components. A part of the soluble content was analyzed by spectrophotometry, and the Fe content in the soluble content was calculated. The remaining soluble content was separated and recovered by distillation into a solvent, an unreacted component, and a reaction product, and the conversion rate of nitrobenzene and the yield of the product N-phenylcarbamate ethyl (EPC) were calculated.

Palladium cylinder inside the reactor (outer diameter 44 mm, height 100 m
m, weight 1.80 g) was installed. In addition, Comparative Examples 3 to 8
Here, a solvent other than aliphatic hydrocarbons was used as the solvent to be mixed with ethanol.

Large Opening 1 A palladium wire mesh (138 x 100 mm, weight 50 g) was fixed in the reactor.

charcoal 1 A palladium block (weight 10 g) was fixed in the reactor.

Example 4 A bucket was attached to a stirrer in a reactor, and 200 g of alumina carrying 5% palladium was filled into the bucket.

Implementation board] As in Example 1, the palladium inner cylinder was fixed in the reactor, but methanol was used instead of ethanol. The reaction yields methyl N-phenylcarbamate as the urethane product.

Implementation Isolated Ruthenium inner cylinder with the same shape as Example 1 (weight 180g)
) was placed in the reactor.

Comparison ■ Instead of installing the palladium inner cylinder in Example 1 above, a slurry in which 5% Pd/C was added to the mixed solvent at a concentration of 4 B-atoms/1 in terms of Pd was supplied into the reactor. Made it react.

Instead of installing the ruthenium inner cylinder in Main Example 6, a slurry in which 5% Ru/C was added to the mixed solvent at a concentration of 4 mg-atom/β in terms of Ru was supplied to the inside of the reactor. I reacted while doing so.

The reaction results are summarized in Table 1 along with the type of solvent used as a mixed solvent with ethanol and the method of fixing the platinum group metal.

(Leaving space below) As is clear from the results in Table 1, according to the method of the present invention, by conducting the reaction in the presence of an aliphatic hydrocarbon solvent, almost all of the Lewis acid as a cocatalyst is insoluble. It can be recovered as a fraction, and the reaction results are completely comparable.

For example, Comparative Example 3 is a conventional example in which ethanol was also used as a solvent, but this and Example 1 showed exactly the same reaction results, indicating that the coexistence of n-hexane did not adversely affect the reaction. It was done. When the solvent was other than an aliphatic hydrocarbon, as shown in Comparative Examples 3 to 8, the amount of Lewis acid eluted was extremely large.

In addition, in Comparative Examples 1 and 2, in which the platinum group metal of the main catalyst was supplied as a slurry without being fixed, the platinum group metal was supplied as a slurry, which caused wear due to jamming in the valve, and the airtightness of the reaction system was impaired. It was difficult to maintain.

(Effects of the Invention) According to the method of the present invention, aromatic urethane is produced from an aromatic nitro compound, a hydrous acid group organic compound, and carbon monoxide in the presence of a catalyst system consisting of a platinum group metal-Lewis acid-ligand. During production, the reaction is performed with the platinum group metal as the main catalyst fixed in the reactor in advance without being supplied from the outside, and an aliphatic hydrocarbon solvent is also allowed to coexist in the reaction system.

As a result, there is no need for the troublesome work of recovery, drying, and optional regeneration of the main catalyst after the reaction, which was essential in conventional methods in order to continue supplying the main catalyst with the reaction substrate. There is no rate drop.

Further, in the conventional method, a considerable amount of expensive platinum group metal is lost during recovery, but in the present invention, the amount of loss is extremely small. Furthermore, the platinum group metal fixed in the reactor can maintain high catalytic activity for a long period of time, comparable to conventional catalysts.

In conventional methods, when the catalyst is separated by filtration, a considerable portion of Lewis acid, which is a co-catalyst, remains in the filtrate, causing product deterioration when the product is separated by distillation.
In the method of the present invention, the Lewis acid can be made substantially insolubilized, and almost the entire amount of the Lewis acid can be recovered as insoluble matter.

As a result, it is possible to prevent contamination and deterioration of aromatic urethane products by Lewis acids, improve the quality and yield of aromatic urethane as the main raw material for the next process, and improve the recovery rate of Lewis acids. , the catalyst can be reused with minimal replenishment of new catalyst. Further, the aliphatic hydrocarbon solvent used can be recovered by distillation from the filtrate containing the urethane product and used repeatedly.

As a result of the above, in the conventional method, it was necessary to add a certain amount of both the main catalyst and the co-catalyst when reusing them, but in the case of the present invention, this is not necessary or is very small. The process of the present invention is economically very advantageous in terms of both catalyst efficiency and work efficiency, and can provide products of excellent quality.

[Brief explanation of the drawing]

Figure 1 is a graph showing the decrease in thermal stability of aromatic urethane (RPC) due to the coexistence of Lewis acid (FeC(!:+)); and Figure 2 is a graph showing the decrease in thermal stability of aromatic urethane (RPC) due to the coexistence of Lewis acid (FeC(!:+)); It is a graph showing the relationship between the amount of FeCQs added as a co-catalyst and the phenyl urethane yield for the case (•) and the case (0) when Pd/C is added to the reactor without coating by the conventional method.

Claims (1)

[Claims] An aromatic nitro compound, a hydrous acid group organic compound, and carbon monoxide are reacted in the presence of a catalyst system consisting of a platinum group metal as a main catalyst, a Lewis acid as a promoter, and a nitrogen-containing heteroaromatic compound as a ligand. A method for producing an aromatic urethane, the method comprising carrying out the reaction in the presence of an aliphatic hydrocarbon solvent in a reactor in which the platinum group metal is fixed.